A common problem encountered during the manufacture of a semiconductor device is the undesirable creation of corrosion of the metal lines of the semiconductor device. A commonly used metal is a combination of aluminum (Al) and copper (Cu) in which the copper is approximately one half of one percent (0.5%) of the combination.
A significant portion of the metal corrosion of the aluminum copper (AlCu) layers in a semiconductor device is caused by chlorine that is present is a plasma etch process that is used to etch the metal layers. The chlorine is supposed to be removed from the metal layers during post metal etch cleaning processes. However, sometimes the cleaning processes do not efficiently strip the chlorine residues. The chlorine residues that are not removed interact chemically with the metal layers to form corrosion in the form of metal chlorides (e.g., aluminum chloride and copper chloride).
FIG. 1 illustrates an exemplary prior art process 100 that comprises a metal etch process 110, and a post metal etch clean process 120 and a subsequent wet tool clean process 130. The metal etch process 110 is carried out by a plasma etch process that contains chlorine. For example, the metal etch process 110 may comprises a process that utilizes a plasma to etch the aluminum of an aluminum metal interconnect stack in a semiconductor device. One example of a plasma etch formulation that contains chlorine comprises boron trichloride and nitrogen and chlorine (BCl3+N2+Cl2).
After the metal etch process 110 has been completed a post metal etch clean process 120 is performed. The post metal etch clean process 120 is designed to remove the chlorine from the metal surfaces. A subsequent wet clean tool process 130 is then applied to provide additional cleaning of the surfaces of a wafer that contains the semiconductor devices. The wet clean tool process 130 removes additional amounts of residual chlorine.
The post metal etch clean process 120 and the wet clean tool process 130 may not remove all of the chlorine that is left on the wafer from the metal etch process 110. The chlorine reacts chemically with water vapor that is present in the atmosphere and combines with the metal surfaces to form metal chlorides. When the chlorine combines with aluminum then aluminum chloride is formed. When the chlorine combines with copper then copper chloride is formed. When the chlorine combines with an aluminum copper mixture then a mixture of aluminum chloride and copper chloride is formed.
The interaction of chlorine with the metal material creates several different types of corrosion of the metal portions (e.g., metal interconnect lines) of the semiconductor device. One type of corrosion occurs when aluminum (Al) and copper (Cu) are exposed to Chlorine (Cl) and water (H2O). FIG. 2 illustrates a photograph 200 showing an example of one type of metal chloride corrosion formed on a metal line due to the presence of chlorine. The corrosion process may occur during the post metal etch clean process 120 and later during the wet clean tool process 130.
It would be desirable to have an efficient method for detecting the presence of metal corrosion due to chlorine during the manufacture of semiconductor devices. One prior art approach to detecting the presence of chlorine induced corrosion involves the use method that is called the “wet box test.” The wet box test typically used by plasma etch engineers to determine whether or not a semiconductor wafer has metal corrosion on it.
The wet box test comprises exposing a semiconductor wafer that is to be tested to a very humid atmosphere (i.e., an atmosphere having a high level of water vapor in it). The wafer is placed in the very humid atmosphere (or even immersed within a container of water) and left for an extended period of time. The wet box test can take from six (6) hours to twenty four (24) hours. Then the wafer is removed, dried and inspected. If there is no visible corrosion then the wafer has successfully passed the test. The wafer fails the test if corrosion is found.
The results of the wet box test are very qualitative. The wet box test is also rather time consuming. Therefore, it would be advantageous to have a more efficient system and method for determining the presence of chloride content and concentration in a semiconductor wafer that is induced by a metal etch process.
Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as future uses, of such defined words and phrases.